T-Nut fasteners consisting of a tubular barrel and a generally peripheral flange at one end, are well known. They are particularly useful in the furniture industry. In this case they are embedded into a work piece typically an element of a piece of furniture which may be made of wood or composition or in fact thermo-plastic in some cases. When the furniture is assembled, bolts or other threaded fastening devices are inserted into the T-Nuts to hold two components of furniture together. Any one piece of furniture may incorporate a large number of T-Nuts, and it will be readily understood that the use of such T-Nuts is wide-spread and on a very large scale. Such T-Nuts are formed by stamping them out of sheet metal, so that the barrel is extruded from the plane of the sheet, and the flanges are cut out from the sheet, so as to form an integral one piece sheet metal T-Nut. The barrel is usually internally female threaded either along its whole length or along a portion of its length. In some cases the free end of the barrel may be provided without threads so that it can be swaged or flared out to provide as it were a rivet action, holding the T-Nut in the work piece. Such T-Nuts are in a great majority of cases provided with spikes, usually four spikes, which are formed by cutting edges of the flanges, to form a series of pointed spikes or prongs which are then bent usually at right angles to the plane of the flange. These prongs embed in the workpiece and provide further security to hold the T-Nut in position.
All these facts are very well known in the industry and are merely repeated here for the sake of clarity and explanation. Numerous patents show various forms of T-Nuts, some of which are listed at the end of this description.
From this explanation it will be understood that the insertion and securing of the T-Nuts in the work piece must be carried out at high speed and with great accuracy and repeatability. Numerous machines have been developed for this purpose to provide automatic power insertion of T-Nuts into a work piece. Many of these machines also provide the swaging or flaring action to flare the free end of the barrel.
Usually such T-Nuts are packaged loose in large containers. They are dumped from these containers into feed hoppers on the insertion machines. They are delivered usually along a feed slide extending from the hopper to the insertion anvil or hammer which drives the T-Nut into the work piece.
It will be understood that continuity and repeatability of operation in such a machine are absolutely essential to provide smooth flow of production of finished product. If there is any holdup in such a machine it may slow down production for minutes or even hours while the machine is made serviceable once more. This downtime causes loss of production, frustration in employees, and may cause missed delivery dates.
One of the leading causes of problems in such machines is that the edge flanges of the T-Nuts, being stamped out from sheet metal, are formed with minute burrs at various points. These burrs become more aggravated as the stamping dies become worn.
The edges of the flanges are sharp, and in most cases are formed in a linear fashion. In many cases the flanges are octagonal. In other cases, they are simply round.
All such flanges do experience certain problems in achieving a smooth flow of T-Nuts along the feed slide, and stoppages are experienced in a random fashion when using insertion machines with such T-Nuts.
One of the problems in such feed slides is that they are usually formed around a curved path. There must therefore be a certain amount of clearance within the slide, to allow for the planar flange to pass around a curved path. There is often a tendency for the flange of one T-Nut to ride up over the flange of a leading or trailing T-Nut, and this then causes jamming of the T-Nuts in the slide and malfunction of the machine.
One approach to overcoming this problem is shown in U.S. Pat. No. 4,508,478, entitled T-Nut Fastener Member, inventor: Herbert E. Leistner, Toronto, Canada, granted Apr. 2, 1985.
In this T-Nut, the leading and trailing flange edges are formed with a generally U-shaped depression. The U-shaped depressions of adjacent T-Nuts function to prevent the over-riding of the flange of one T-Nut with the next, in the slide.
While this improved T-Nut greatly reduces the problem, it has been found desirable to provide still further enhancements. This will be of significance where the T-Nuts are going around a track which exhibits a compound curve. In these cases the T-Nuts may have a tendency to twist slightly from side to side. As a result of this twisting one T-Nut flange may still on occasion jam with the next T-Nut flange. While this occurrence is relatively rare, it will be appreciated from the above explanation that any malfunction of the insertion machine is undesirable.